Sep 09, 2002 APPLICATION NOTE 1193 Electronic s Comparison Abstract: This note compares advantages and disadvantages of Cathode Ray Tubes, Electro-Luminescent, Flip- Dot, Incandescent Light Bulbs, Liquid Crystal, Light Emitting Diode, Organic LEDs, Polymer LEDs, Glow Discharge, Plasma Panels, and Vacuum Fluorescent technologies. This note compares the main electronic s technologies in the table below. Each type is described briefly, and the relative advantages and disadvantages are reviewed. Type Cathode Ray Tube Electro- Luminescent Acronym Emissive or Reflective CRT Emissive The CRT is a vacuum tube using a hot filament to generate thermo-electrons, electrostatic and/or magnetic fields to focus the electrons into a beam attracted to the high voltage anode which is the phosphor coated screen. Electrons colliding with the phosphor emit luminous radiation. Color CRTs typically use 3 electron sources (guns) to target red, green, and blue phosphor patterns on the screen. ELD Emissive EL s are solid state s which use a phosphor to emit light in the presence of an electric field. Phosphors used are usually yellowo or green. Technology Advantages Disadvantages Very bright Wide viewing angle No mask, so no pixel size limitation for mono Minimum pixel size 0.2mm (color) Low cost standard sizes Low cost highres color Moderate (20khrs+) Flat panel Bright, light emitting mono s High (5kV to 20kV +) drive Not a flat panel (rare exceptions) Can be fragile, particularly neckend Heavy Source of X-rays unless screened Affected by magnetic fields Difficult to recycle or dispose of 150V+ operating Color panels difficult to make Development largely overtaken by PDPs
Flip-Dot Reflective Each pixel comprises a hinged disk. The disk is matt black on one side (unlit), and fluorescent or reflective on the other (lit). Various techniques are employed to flip the disk. One method balances the disk around an electromagnetic soft iron armature. The winding is energized one way or the other to attract the disk to one side or the other. Remanent magnetism holds the position, so only a short power pulse is required to flip the pixel. Only draws power during a transition Retains pattern when off Very wide Low cost for large segments Can have long (100khrs+) High power required to change pixel state Difficult to make segments smaller than 8mm diameter Limited to mono color Requires some ambient light to be visible Incandescent Light Bulb Emissive A coated tungsten filament is run white hot in vacuum, and it radiates both visible light and infrared (heat). Mature technology, very available Lowest cost for moderate to high light output Standard sizes easy to obtain Short (1khrs to 10khrs); socket adds cost Usually inefficient compared with LED Narrow operating voltage High peak current when starting Usually run hot Usually fragile Liquid Crystal LCD Reflective An LCD uses the properties of liquid crystals in an electric field to guide light from oppositely polarized front and back plates. The liquid crystal works as a helical director (when the driver presents the correct electric field) to guide the light through 90 from one plate through the other plate. Small, static, mono panels can be very low cost Both mono and color panels widely available Static panels offer lowest power/voltage Reflective panels in general are low power Very easy custom segment shapes, sizes Reverse backlit mono panels are attractive Backlight adds cost, and often limits the useful Requires AC drive waveform Fragile unless protection added temp (0 C - 50 C) Temperature compensation usually required Low yields raise cost for larger (17"+) s
Light Emitting Diode LED Emissive LEDs are photon emitting semiconductors which emit light due to the injection electroluminescence effect. The wavelength of the emitted light varies primarily due to the choice of semiconductor materials used, and is commonly in visible spectrum or infrared. Lowest cost red or green emissive indicator Available in very small sizes Very bright versions available (higher cost) Red and green types work from 3V supply LED is point source, so light shaping required to make segment shapes White and blue LEDs expensive, need >3.6V supply Color and efficiency vary with and current Care required to achieve 50 khrs+ Organic LEDs Polymer LEDs OLED PLED Emissive These s use organic electroluminescent materials deposited on a glass or flexible substrate. Devices based on small molecules are usually referred to as OLEDs. Those based on large organic 'polymer' molecules are usually called PLEDs. Light is generated by injection electroluminescence, like LEDs. The choice of organic material sets the emission color OLED pixels are capacitive (tens to hundreds of picofarads) leading to significant switching losses for large s with high multiplex ratios. Moderate cost for small (<4") color panels Wider viewing angle than LCD Faster element response than LCD Emissive, unlike LCD color panels RGB and mono s Can be built on a flexible substrate 6V to 16V operating Differential aging effects limit Power consumption high for matrix panels >128 x 64
Glow Discharge (Plasma) Indicators Nixie Emissive A high voltage between two electrodes encapsulated in a tube with an inert gas (typically neon) ionizes the gas allowing current to flow and a glow discharge to appear around the cathode. If the tube is driven from an AC source (e.g., a neon indicator), the glow discharge appears around both electrodes. Complex s use multiple cathodes shaped either as segments (one or more lit to make a character) or complete numerals (one lit at a time). No phosphor (gas choice sets discharge color) Long (40khrs+) AC or DC operation (indicators) Unregulated DC operation (digits) Obsolete but for specialized applications Not suitable for small, detailed 40V to 150V operating Plasma Panel PDP Emissive Plasma s use multiple controlled gas discharge paths (one path per color per pixel) but the inert gas is chosen to glow outside the visible spectrum. Each local current discharge path terminates with its own phosphor coated cathode, which in turn emits luminous radiation. The cathodes can be ard as RGB triads to make a color. Very bright, thin, color Available in large (30"+) sizes Wider viewing angle than TFT color LCD Phosphors limit (5khrs to 20khrs) 150V+ operating Moderate power consumption Entire must be exercised to avoid phosphor differential aging effects
Vacuum Fluorescent VFD Emissive The VFD is a vacuum tube using hot filaments to generate thermoelectrons, A grid (static type) or multiple grids (multiplexed type) control and diffuse the thermoelectrons, which are attracted to one or more high voltage phosphor coated anodes, which then emit light. The anodes are at the back of the, so the emitted light passes through the grid(s) and filaments and the front to be seen by the user. The filaments are not run hot enough to be usually visible. Long (40khrs+) Wide viewing angle Very bright, attractive, typically green Very easy custom segment shapes, sizes Different colored segments easy 12V grid/anode voltage versions available Filament supply (±8% typ. tolerance) required 10V to 60V grid/ anode operating RGB s available, but expensive Phosphors other than green limit